1. Field of the Invention
The present invention relates to a broadcast receiving device for receiving a broadcast signal and a method of controlling the broadcast receiving device.
2. Description of the Related Art
In digital terrestrial broadcasting, scrambled video content is transmitted. Video content scrambling is performed using a conditional access system (CAS). Currently, a BS conditional access system (B-CAS) using an IC card is in operation.
Methods of protecting video content (especially, content copyrights) in broadcast receiving devices are called “rights management and protection (RMP)”. The RMP methods include a method of encrypting video content using an encryption key. For example, in the currently used B-CAS, three kinds of encryption keys, i.e., a scramble key, a work key, and a master key are used in a hierarchical manner (refer to the standard ARIB STD B-25 Ver. 5.1).
In “Part 3: Reception Control System (Content Protection System)” in the standard ARIB STD B-25 Ver. 5.1, a new content protection system (hereinafter, referred to as “new RMP system”) is standardized. In the new RMP system, three kinds of encryption keys, namely, a scramble key, a work key, and a device key are used in a hierarchical manner.
According to the new RMP system, each operating broadcast station transmits an entitlement management message (EMM) for work key setting and an entitlement control message (ECM) for scramble key transmission to a broadcast receiving device at predetermined intervals.
In this instance, each EMM is data carrying information specific to the broadcast receiving device. The EMM includes ID (device ID) to identify the broadcast receiving device and a work key to decode the corresponding ECM.
Each ECM is data carrying information common to all broadcast receiving devices. The ECM includes a scramble key to decode video content, and program information.
The ECM is encrypted using the work key which varies from one RMP entity to another. The EMM is encrypted using the device key which varies from one device ID to another. The broadcast receiving device receives the EMM, which the device should receive and which is periodically transmitted, and sets the work key. To view a program, the broadcast receiving device receives and processes the ECM to acquire the scramble key and then descrambles video content.
In the new RMP system, if the operation of the system is significantly affected by, for example, the appearance of an unauthorized broadcast receiving device manufactured without a license from an RMP management center, a measure called “revocation” is performed. In revocation, device keys and work keys are updated. In this instance, each authorized broadcast receiving device can acquire the updated device key and work key but the unauthorized broadcast receiving device cannot acquire the updated keys. Accordingly, the unauthorized broadcast receiving device cannot descramble video content.
An EMM for a broadcast receiving device having certain device ID is broadcasted at regular intervals. If the device keys and the work keys are updated, therefore, it may take considerable time between the start of receiving a broadcast signal and acquisition of the work key in the broadcast receiving device. Disadvantageously, the broadcast receiving device cannot play video content back until the device acquires the work key. A user is therefore fallen into a program unviewable state where the user cannot view a program.
In consideration of the above-described problems, there is proposed a method of connecting a broadcast receiving device to a network, acquiring a detailed message from a server upon occurrence of a work-key unset error (when a necessary work key does not exist), and displaying the message in an on-screen display (OSD) manner. Japanese Patent Laid-Open No. 2006-135589 discloses such a method.
The method disclosed in Japanese Patent Laid-Open No. 2006-135589 does not specially take a work key acquiring procedure into consideration. Disadvantageously, the method does not respond to user demands to get out of the program unviewable state as soon as possible.